There is considerable demand for high-refractive-index, high-dispersion optical glass. In particular, aspherical lenses comprised of such glass are indispensable as high-performance, digital still camera-use lenses.
The precision press molding method (also called the “mold optics pressing method”) is a known method of producing large quantities of aspherical lenses. Phosphate-based glasses are known as a high-refractive-index, high-dispersion glasses that can be molded by precision press molding. Phosphate-based optical glasses are good glasses, but present a problem in that the glass surface tends to scratch during precision press molding.
The glasses disclosed in Patent References 1 to 5 are known non-phosphate-based, high-refractive-index, high-dispersion optical glasses. These glasses all have silica-based compositions.